1. Field of the Invention
The present general inventive concept relates to a method of writing a reference servo signal of a hard disk drive, and more particularly, to a method of writing a reference servo signal of a hard disk drive by which the hard disk drive by itself can write the spiral reference servo signal, and an apparatus suitable therefor.
2. Description of the Related Art
In general, a hard disk drive that is a data storage media reproduces data recorded on a disk or writes data to a disk using a magnetic head. As the hard disk drive gradually increases in capacity and density, while being made compact, BPI (bit per inch), which is a density of data in a rotational direction of the disk, and TPI (track per inch), which is the density of data in a radial direction of the disk also increase. As a result, a more accurate control mechanism is needed for the hard disk drive.
The hard disk drive includes an HDA (head disk assembly) and a PCB (printed circuit board) assembly to control the HDA. The HDA includes a head for storing or restoring information, a disk on which the information is recorded, a spindle motor for rotating the disk, an actuator arm and a VCM (voice coil motor) for moving the head, and an ODCS (outer disk crash stop) and IDCS (inner disk crash stop) for restricting a range of movement of the actuator arm. The ODCS and IDCS are bumping units which restrict the range of movement of the actuator arm to prevent the head from moving to a position where servo information of the disk is not recorded.
In order to control the position of the head on the disk, the servo information (i.e., position information) is recorded for each track. As the recording density of the hard disk drive increases, a total number of tracks increases so that a portion taken by the time needed for recording the servo information on the disk of an entire process time is gradually increased.
A conventional servo writing method to record the servo information on a disk in a hard disk drive uses a servo writer having a high precision encoder and a mechanical pushpin. One end of the mechanical pushpin is attached to a master actuator arm and the other end is extended through a slot to the servo writer outside of the hard disk drive. The movement of the mechanical pushpin, that is, the movement of the master actuator arm, is controlled by the high precision encoder and a positioner. In addition, a clock head (not shown) is instructed to record clock information on the disk to provide position information in the rotational direction of the disk. The servo writer controls the position of the head in the radial direction of the disk by the mechanical pushpin and writes a reference servo signal of the disk.
The above described conventional servo writing method has a problem in that the precision of the positional control is deteriorated by non-repeatable run out (NRRO), disk flutter, and vibration of a spindle motor. Furthermore, the use of the servo writer with the positioner/encoder greatly increases costs related to the servo writing method so that an efficiency of production of the hard disk drive is negatively affected.
Servo writing methods developed in an attempt to solve the problem described above include an off-line servo writing method and a self servo writing method. According to the off-line servo writing method, servo information is written on disks in advance using an off-line servo track writing apparatus before the disks are installed in the hard disk drive. This off-line servo writing method can improve precision compared to the conventional servo writing method (described above). However, the off-line servo writing method has problems of an increase of repeatable run out (RRO) generated by an eccentricity of the disk and an increase of an additional track search generated due to a shift between the disks.
On the other hand, according to the self servo writing method, reference servo information is first written on one of assembled disks (i.e., a reference disk) using a servo writer and then final servo information is written on the disks by the hard disk drive itself by referring to the reference servo information written on the reference disk. In this method, a quality of the final servo information is determined according to a precision of the reference servo information. Also, the self servo writing method does not rely on the conventional servo writer (described above), thereby decreasing cost. However, in the self servo writing method, the time for self servo writing increases and a tracing capability based on the reference servo information is weak.
The writing of the reference servo information for the self servo writing method includes a burst method and a spiral method. According to the burst method, a reference servo signal is written radially to the disk and a final servo signal is written by referring to the reference servo signal. According to the spiral method, reference servo signals having a spiral shape are written to the disk and the final servo signal is written by referring to the spiral reference servo signals.
U.S. Pat. No. 5,668,679 published on Sep. 16, 1997, Korean Utility Model Publication No. 87-8922 published on Jun. 13, 1987, and Korean Patent Publication No. 2000-34856 published on Jun. 26, 2000 describe the spiral method in detail.
In writing the reference servo signal, the spiral method is typically faster than any other burst method. However, since the conventional self servo writing methods all use the conventional servo writer (described above) to write the reference servo signal, the cost for manufacturing the hard disk drive is high.
FIG. 1 schematically illustrates a conventional method for recording a spiral reference servo signal 100, which is described in U.S. Pat. No. 5,668,679. Referring to FIG. 1, a spiral reference servo signal writing apparatus includes a disk 12 installed on a spindle motor (not shown) that is rotatable, an actuator arm 24 that can adjust a position of a read/write head 16 attached thereto, two crash stops 17 and 18, and a voice coil 26. When the voice coil 26 is excited and thus the actuator arm 24 moves with respect to the disk 12, the head 16 is located at an arbitrary position between R1 and R2 on the disk 12. R1 and R2 respectively indicate an outer circumferential limit and an inner circumferential limit of the spiral reference servo signal 100. When the signal is written to the disk 12 while moving the head 16 in a radial direction of the disk 12 at a constant velocity between R1 and R2, the spiral reference servo signal 100 is spirally written as illustrated in FIG. 1. Here, T0 represents an index, T1 represents a time offset that the spiral track 100 passes the track position R1 under the head 16, and T2 represents a different time offset that the spiral track 100 passes the track position R1 under the head 16 at a different time than the offset T1.
FIG. 2 illustrates a pattern of writing the spiral reference servo signal 100 to the disk 12. The spiral reference servo signal 100 is written at least as many as a number of sectors in a circumferential direction of the disk 12 (actually two times). Although not illustrated in FIG. 2, the spiral reference servo signal is written while being wound about 20 times between R1 and R2.
R1 and R2 of FIG. 1 indicate the outer circumferential limit and the inner circumferential limit where the spiral reference servo signal 100 can be written, which are respectively referred to as a reference writing start position and a reference writing stop position.
A clock signal (not shown) is provided to indicate an interval of writing the spiral reference servo signal 100, that is, the position on the circumference of the disk 12. The clock signal is written to an outermost circumference of the disk 12 by a clock head (not shown) of the conventional servo writer. The clock head of the conventional servo writer is pulled back into the hard disk drive through another slot.
FIG. 3 illustrates a detailed structure of the spiral reference servo signal 100 written to a disk. The spiral reference servo signal 100 has burst 302 and sync bits 304.
A step of writing a final servo signal by referring to the spiral reference servo signal 100 is referred to as a servo copy step. In the servo copy step, referring to the sync bits 304 illustrated in FIG. 3, the final servo signals are written based on concentric tracks formed by linking the sync bits 304 at the same positions in the radial direction of the disk 12.
In writing the spiral reference servo signal 100 using the apparatus of FIG. 1, the actuator arm 24 is driven by a mechanical pushpin (not shown) and the mechanical pushpin is driven by the conventional servo writer outside the hard disk drive. The conventional servo writer includes an encoder and a position setter to drive the mechanical pushpin. In the burst method, the reference servo signal is written using the conventional servo writer. That is, in the conventional reference servo signal writing method, an external servo writer is needed which extends inwardly into the hard disk drive to precisely control the position of the mechanical pushpin connected to the actuator arm 24. Thus, a high precision encoder and a position setter are required.
In the hard disk drive, since the positions of a slot in which the pushpin of the servo writer is inserted and a slot in which the clock head is inserted are different according to the model type, the conventional servo writer needs to be separately provided (i.e., manufactured) for each model. In the self servo writing method, this necessity of the conventional servo writer increases the manufacturing cost of the hard disk drive.